1. Industrial Field of Utilization
The present invention relates to a thermoplastic resin composition with superior molding property and mechanical strength.
More specifically, the present invention relates to a thermoplastic resin composition as molding material, wherein a polyolefin resin containing a substituted silyl group is mixed with a saturated polyester resin or hydroxyalkylated polycarbonate resin or hydroxyalkylated polyphenyl ether resin, to provide both the molding property of the former resin and the mechanical strength of the latter resin, and further to prevent therein decreases in impact resistance and the occurrence of delamination, which generally develop easily in incompatible resin mixtures to thereby meet the high- standard quality requirements for structural components of automotive and electrical products.
2. Discussion of the Prior Art
Polyolefin resins are resins for wide use in respective fields, which is generally economical and has superior molding property, low moisture-absorption characteristic, organic solvent resistance and low specific gravity. However, its rigidily at high temperatures is not sufficiently satisfactory in terms of its performance.
On the other hand, various resin have been developed as saturated polyester resin and they are generally excellent in rigidity, heat resistance and the like. However, the molding of these resins may sometimes be difficult, due to their hydrolysis during molding. The resins also have a disadvantage such as the deterioration of electric properties, due to their moisture absorption.
Alternatively, polycarbonate resins show excellent rigidity, impact resistance, heat resistance and the like, but their resistance to organic solvents is poor.
Polyphenylene ether resins are useful as resins for molding materials because of their excellent thermal, mechanical and electrical properties. However, they have problems in molding property, organic solvent resistance, and impact resistance, so their range of utilization is limited.
Hence, if there can be obtained a composition with all of the individual resin properties described above whereby the disadvantages are controlled, its industrial significance can be said, to be extremely important.
However, as polyolefin resins are originally incompatible with saturated polyester resins, polycarbonate resins and polyphenylene ether resins, and in addition, do not have affinity there to the simple mixing of a polyolefin resin there with cannot produce good adhesion in the structural interface of the two components. For that reason, the two-phase interface of the product obtained becomes defective, resulting in the reduction in mechanical strength and impact resistance. Also, it is difficult for the two phases to become unifirm or finely disperse, so delamination easily develops when shearing stress is imposed on the phases during molding such as by injection molding. When these incompatible polymers are to be blended, one of the methods that can be thought of to solve the problems insofar mentioned is to compound a third component in order to improve the affinity of the two components.
As regards to the composition comprising a saturated polyester resin and a polyolefin resin, there have conventionally been proposed methods such as using an ethylene copolymer containing epoxy group as a third component in combination with a saturated polyester resin and a polypropylene resin (Japanese Patent Laid-open No. 60744/1986); using a saturated polyester resin, a polypropylene resin modified with maleic anhydride and an ethylene copolymer containing epoxy group in combination (Japanese Patent Laid-open No. 60746/1986); and using an ethylene copolymer containing epoxy group in combination with a modified polypropylene resin produced by graft copolymerization of an unsaturated epoxy compound and a saturated polyester resin (Japanese Patent Laid-open No. 213352/1989).
Even in such compositions, however, the affinity between the modified polypropylene resin and the saturated polyester resin is not sufficient, so that the combined use of an ethylene copolymer containing epoxy group is essential in order to increase impact resistance. however, as a resullt the rigidity then decrreases and it is difficult to achieve a high level of balance between rigidity and impact resistance.
A great number of inventions have been made regarding mixed compounds of polycarbonate resins and polyolefin resins. The compositions with rigidity enhanced by means of simple mixing of a polycarbonate resin and a polyolefin resin, have been suggested in Japanese Patent Publication No. 13664/1965 and Japanese Patent Laid-open No. 223741/1984. In both, rigidity has been successfully improved to a certain degree. However, the compatibility between the two components is extremely low, so the resulting two-phase interface may have some defects, leading to a decrease in mechanical strength and impact resistance. As it is difficult for the two phases to become uniform or finely dispersed, delamination may readily occur when shearing stress is imposed during molding such as by injection molding, resulting in severe damage to the appearance of the molded product, so that practial use thereof is hard.
Examples for using modified polyolefin resins so as to improve the compatibility between polycarbonate resins and polyolefin resins are illustrated in Japanese Patent Laid-open Nos. 123251/1982 and 125253/1982, both employing ethyleneglycidyl methacrylate copolymers, and Japanese Patent Laid-open No. 223742/1984 employing polypropylene resin modified with unsaturated carboxylic acid. However, the terminals of polycarbonate resins are generally sealed by using terminal stoppers or molecular weight modifiers (for example, monovalent phenols such as p-tertiary butylphenol, phenol and the like), or by using long-chain alkylphenols to modify fluidity, so the effect of a modified polyolefin resin alone on compatibility is not enough.
The present inventors previously found that compositions with excellent properties can be obtained by adding a polycarbonate resin having an aliphatic hydroxyl group at its terminal, together with a polypropylene resin containing carboxyl group or epoxy group to a blend of polycarbonate resin and polypropylene resin, and disclosed the findings in Japanese Patent Laid-open Nos. 215752/1988 and 215749/1988, separately.
In the technique of using a polypropylene resin containing malic anhydride and a polycarbonate resin containing terminal hydroxyl group, as disclosed in Japanese Patent Laid-open No. 215752/1988, further increases in the compounded amount of the polypropylene resin containing maleic anhydride in such a composition so as to further improve the properties thereof can modify the compatibility, resulting in the formation of fine dispersion, but mechanical strength such as impact strength decreases after passing its maximum point.
The production process of polypropylene resin containing glycidyl methacrylate disclosed in Japanese Patent Laid-open No. 215749/1988 is complex, so that there has been a demand for an economical production technique thereof.
In regards to the composition of a polyphenylene ether resin and a polyolefin resin Japanese Patent Publication No. 7069/1967 proposes a blend comprising a polyolefin resin and a polyphenylene ether resin, but the organic solvent resistance and mechanical strength successfully meeting the high level demands required in the industrial field are not necessarily satisfied by this blend. Furthermore, Japanese Patent Laid-open Nos. 71158/1978, 88960/1979 and 100159/1984 propoose to compound, for example, a block copolymer of styrene and butadiene or the hydrogenated products thereof, for the purpose of improving the compatibility of polyphenylene ether resins and polyolefin resins. However, the organic solvent resistance of the polyolefin resin is not sufficiently exerted therein, because of the small amount of polyolefin resin compounded and the substantially continuous phase of polyphenylene ether resin. Japanese Patent Laid-open Nos. 103557/1983 and 76547/1985 each disclose compositions compounded with not less than 20 wt. % of a polyolefin resin, and also compounded with a diblock copolymer comprising for example an alkenyl aromatic compound and conjugated diene, and the hydrogenated product thereof, as compatible agents. Tensile properties and brittleness are improved in the compositions, but the required levels regarding rigidity and thermal resistance cannot be satisfactorily met.
One of the present inventors previously found that a propylene-dialkenylbenzene copolymer modified with styrene monomer is effective as an affinity modifier for polyphenylene ether resins and polypropylene resins, the modified propylenedialkenylbenzene copolymer being obtained by polymerizing, with a styrene monomer in the presence of an initiator of radical polymerization, a crystalline propylene-dialkenyl benzene copolymer obtained by copolymerizing propylene as a main component with a small part of a dialkenylbenzene compound. The inventor disclosed the finding in Japanese Patent Laid-open No. 170647/1989. However, the effects of the addition are not satisfactory in the propylene-dialkenylbenzene copolymer modified with styrene monomer under conditions of radical polymerization; if an amount enough to modify the affinity is added, impact strength is improved, although this involves a problem that rigidity, specifically high-temperature rigidity is lowered, so that further improvement is desired.
The object of the present invention therefore is to provide a resin composition for molding comprising a homogeneous blend of a polyolefin resin with a saturated polyester resin, or a polycarbonate resin, or a polyphenylene resin, in which delamination which is often observed at the molding stage when blending incompatible resins is controlled and in which the final molded products thereof have good appearance and improved mechanical properties, in particular impact strength.